Art of producing metallic zinc



(N0 Mdel.)

P. c. GHOATB.

ART OF PRODUCING METALLIC ZINC. No. 518,732. Patented Apr.i,24, 1894,.

fave 71707" V Z f r (SQ-{Locals UNITED STATES PATENT. OFFICE.

PARKER C. GHOATE, OF NEW YORK, N. Y., ASSIGNOR TO THE ELECTRICAL ZINCCOMPANY, OF NEW JERSEY.

ART OF PRODUCING METALLIC ZINC.

SPECIFICATION forming part of Letters Patent No. 518,732, dated April24, 1894. Application filed January 21, 1892. S rial No. 418, 842%. (Nspecimens.)

To a whom it may concern.-

Be it known that I, PARKER O. CI-IOATE, a citizen of the United States,residing in the city of New York, in the countyand State of New York,have invented certain new and useful Improvements in the Art ofProducing Metallic Zinc, (Case N o. 4,) of which the following is aspecification.

, My invention relates generally to the production of zinc from its oresand the object of my improvements is to. provide an economical method ofproducingcommercially pure metallic zinc. While my process may beapplied to the 1 production of zinc as a metal from any of its ores, itis more especially valuable when employed in connection with the largeclass of ores known as blendous or complex which contain besides zincnumerous other metals such as gold, silver, iron, lead, arsenic,antimony, bismuth, cadmium, 850., in varying proportions, and which onaccount of the difficulty of working them economically have heretoforebeen discarded at the mines in great quantities as waste products. Inworking such ores for the extraction of metals other than zinc, asheretofore practiced there has been a total loss of. the zinc, exceptwhen utilized as a pigment, and at the same time its presence causesheavy losses of the other metals such as gold, silver, 850. Although inmany cases these ores arevery rich in zinc, which is often the mostvaluable constituent, all attempts to treat them for the extraction ofthat metal commercially have failed even at the expense of the sacrificeof the other constituents of value. Thus the ordinary method ofproducing metallic zinc from the ore by distillation is entirelyinapplicable to 40 these complex ores, since so many other metals aredistilled with the zinc and enter as impurities into the metallicproduct as to make it undesirable for the commercial uses to whichmetallic zinc is applied.

Although numerous attempts have been made to that end no method has beenheretofore devised by means of which it has been possible tocontinuously produce pure metallic zincon a profitable commercial scale,by electrolytic deposition. The difficulty in utilizing electrolysis asa means of producing pure metallic zinc is primarily due to the factthat zinc is electro-positive to many of the metals which are presentwith it in the ore and so much so as to deposit or precipitate uponitself from acid solutions most of these metals, and if any such metalsbe allowed to be present in the bath in solution with the zinc they willbe deposited with it and appear as impurities in the product. In depos-6o itingzinc from solutions of its salts free acid quickly appears inthe bath through the action of the current upon the solution and, un- 7less neutralized or annulled, soon brings the operation to a stand stillby re-dissolving the zinc from the cathode as fast as it is depositedthereon. Hence even though a pure zinc solution be originally formed andthe operation of depositing a pure metallic zinc be begun it can only bemaintained and carried on by 7c neutralizing or annulling the free acidand in such a way that soluble, depositable impurities shall not enterinto the bath, where they will be a source of prohibitory trouble andexpense. By my improvement I overcome these difficulties, for it is aresult of my process that the condition in which I take the zincwherewith to maintain the electrolytic solution enables me to neutralizethe acid set free in the bath in an efficient and economical manner andat the same time to maintain the solution in its original state, withoutthe continued use of precipitants or other similar means ofpurification.

The defects of prior electrolytic processes have largely come from thefact that in regenerating the solution the ore itself was used as theneutralizing agent for annulling the free acid so that all solublematter present with the zinc in the ore went into the solu- 0 tion asoften as it was regenerated and had to be continually removed therefrom.In my process on the contrary, I, at the outset take the zinc in a statefrom which all the soluble impurities can easily be eliminated before 5the zinc goes into solution, while such insoluble impurities as go intothe electrolytic baths will readily separate themselves out during theworking of the charges, so that in this way I am able to annul the freeacid in the mo bath and maintain a practically pure and nearly neutralsolution for the action of the electric current.

tilize any of the zinc or lead contents.

From the point of View of my process, a pure solution is one which isfree from those metals which would be electrolytically deposited beforeor along with the zinc and would thus enter into and contaminate theproduct.

To the end therefore of maintaining the purity of solution referred tomy invention consists broadly in producing a commercially pure metalliczinc by depositing the zinc by electrolysis from an aqueous acid zincsalt electrolyte, maintained and regenerated by dissolving in the acidset free in the bath by the electric current an oxidized zinc fume freedfrom its impure soluble constituents which are more volatile than zinc,such as the oxides of antimony, arsenic, cadmium, &c.

The accompanying drawing shows a sectional elevation of a form ofapparatus which may be used in connection with my process, containing avessel in which the solution is formed, and the baths for theelectrolytic treatment of it, together with feed and overflow tanks, andalso a pump and connecting pipes for keeping the solution incirculation.

Any usual or suitable mode may be adopted for obtaining the zinc fume tobe used in my process. As an example of one well known method, the oremay be first crushed and then when it contains an excess of sulphur, itmay be roasted ata moderate temperature not sufficiently high tovolatilize the zinc, in order to drive 01f the excess of sulphur. Thepartially desulphurized ore may then be mixed with carbonaceous fuel,such as coal screenings in a furnace in which air is admitted beneathits grate, and may be roasted at a temperature high enough to volatilizethe zinc until the zinc contained in the ore is driven ofi. Thevolatilized zinc and other volatilized bodies may then be caught andcollected in a bag room in the ordinary manner. The resulting productwill be substantially pure oxide of zinc in the shape of a fine powderknown as fume, mixed with such lead as was volatilized with the zincwhen lead occurs in the ore. There may also frequently occur with thezinc and lead fume, as condensed products, other volatilizableconstituents, which may have been present in the ore, such as the oxidesof antimony, arsenic, cadmium, 850. These constituents are allvolatilizable at a lower temperature than zinc and lead. Hence when theyoccur in appreciable quantities I dispose of them by subjecting the fumeto a moderate heat at a temperature of from 500 to 800 Fahrenheit in anywell known form of muffle furnace, thereby revolatilizingsuch morevolatile constituents, care being taken not to apply sufficient heat torevolameans of this roast the fume is purified from its more volatileconstituents, thereby easily eliminating all those impurities which aresoluble in the electrolyte employed and which would otherwise enter intosolution with the zinc and contaminate the deposited product.

Other metals which may have been contained in the ore, such as iron,gold, silver, &c., are not driven off with the volatilized product butremain in the furnace in the form of cinder or slag and may afterward besmelted out and recovered in the usual manner.

I do not confine myself to the above described mode of producing orpurifying the zinc fume, as this may be done in any suitable way, itbeing only necessary to my invention that I should have for maintainingthe electrolytic bath by regenerating the same and annulling the freeacid therein, a zinc product of such a nature chemically that it willnot carry to the bath an acid molecule for example a zinc salt and onewhich is properly purified from the soluble impurities contained in theore. The zinc solution to be subjected to electrolysis may be primarilyprepared by forming a solution of a zinc salt or salts in any usual orsuitable manner and with any suitable acid or mixture of acids providedonly that the solvent acid used is not a solvent of lead where lead ispresent in the zinc product used in regenerating the solution; thus thesolution may be prepared by dissolving metallic zinc in dilute sulphuricacid, or sulphate of zinc in water. In case the solution as firstprepared contains in solution any impurities which would be depositedwith the zinc upon the cathode, they must be removed from the solutionbefore the production of pure zinc canbe begun. This may be done bypassing a current through the solution until all the impurities aredeposited upon the cathode or precipitated out. The impure deposit orprecipitate thus obtained should then be removed and if carrying zincmay be returned to the roasting furnace for volatilization andpurification. I may however obtain a pure solution in the first instanceby the use of the purified zinc fume already described. For this purposethe fume is mixed with dilute sulphuric acid as a solvent, in a treatingtank shown in the drawing at A, in such proportions as to form aconcentrated solution. The zinc will be dissolved, while the otherconstituents such as the lead sulphate, &;c., which constitute the onlyimpurities now remaining, being insoluble are not acted upon andconsequently sepa rate out and settle to the bottom of the tank, leavinga clear solution which contains of all the elements originally presentin the core, only the zinc, from which the others will now havebeenseparated by the preceding steps of the process. The clear solutionis next drawn off through a pipe seen in the drawing at 1, into a feedtank B, whence it is conveyed to the electrolytic baths 0, c, o, bypipes 2, 2, 2, opening into the bottoms of the baths. The pure solutionis now ready for the depositionof the zinc contained in it by theapplication of the electric current. For this purpose the baths aresupplied with anodes of suitable material such as lead or carbon,insoluble'in the solution and cathodes which may be plates of zinc orcopper.

The anodes and cathodes are connected with mains L L, leading from asuitable source of electricity D, such as a dynamo of proper capacity.If desired the solution may be heated to lower the resistance of thebaths. Current is now applied and zinc from the solution is depositedupon the cathodes. As the zinc is deposited free acid is liberated inthe baths and being lighter than the solution rises to the surface. Inorder to neutralize the free acid and at the same time maintain theoriginal degree of purity and gravity of the solution, the free acid isdrawn from the baths through overflow pipes, 3, 3, 3, and carried to atank E. The treating and feed tanks and the baths and overflowtanksshould be set upon different levels so as to produce a natural flowfrom the treating tank and through the baths and thence to the overflowtank. By means of a pump P the acidulated solution in the tank E israised to the treating tank A, through the pipe 4. It is thereneutralized by the addition to it of a fresh supply of purilied zincfume, the zinc being soluble in the dilute free acid, After anyinsoluble constituents of the fume have settled out the solution is ledto the feed tank B and thence, as required, to thebaths to maintain thesolution therein. Since 'the overflow from the baths will contain aconsiderable proportion of zinc a portion of it may if desired bereturned directly to the feed tank B, through the pipe 5 to be passedagain through the baths instead of being regenerated in the firstinstance. In

this mannerl easily and effectually annul the free acid, and maintainthe solution in its original state, sinceI always have a sufficientsupply of purified zinc fume therefor,and thus enable the process to becarried on indefinitely. At the same time I maintain a continualcirculation through the baths and prevent the stratification of the acidwhich would take place if the solution were not kept in motion.

In case there should be small amounts of zinc salt in the oxidized zincfume used in annulling the free acid it will not seriously interferewith the operation of the process since any difficulties that mightarise from its presence may be easily obviated by removing a smallportion of the solution from time to time and substituting water in itsplace. There will practically be no loss of Water will have to be addedto the solution from time to time in small quantities to supply theslight loss that will take place. The deposited zinc may be stripped oithe plates and melted, or where zinc plates are used as cathodes theplates may be melted whenever a sufliciently heavy deposit has beenformed upon them.

Any other convenient electrolytic apparatus may be employed, and I wishit to be understood that I do not limit myself in any portion of myprocess to any particular form of apparatus for putting it intopractice. Nor does the manner oforiginally preparing the electrolyte tobe used nor the degree of purity attained therein form any part of mypresent invention which is directed particularly to regenerating thebath by neutralizing thefree acid liberated therein in such a way as tomaintain the solution in its origina purity.

The advantages of my invention will be readily apparent to those skilledin the art since it enables the easy and economical production of zincfrom its ores, and by its use vast quantities of ore heretofore wasteand of no value can be reduced to their component metals and madevaluable.

Having thus made known my improvement, what I claim as new, and desireto secure by Letters Patent, is

1. The hereinbefore described process of continuously producing metalliczinc by electrolysis, which consists in depositing the zinc from anacidulated solution of a zinc salt, drawing 06 from the bath the freeacid liberated therein, dissolving in such acid oxidized zinc, in thestate of fume, freed from its more volatile soluble impurities, andreturning the solution thus formed to the bath from time to time, asrequired, to maintain the electrolyte, substantially as set forth.

2. The hereinbefore described method of maintaining and regenerating anacid zinc electrolyte which consists in dissolving in the acid set freein the bath during electrolysis oxidized zinc in the state of fume,freed from its more volatile soluble impurities, and maintaining theelectrolyte with the solution thus PARKER C. CIIOATE.

Witnesses:

BENJAMIN BARKER, .Ir., OLARKsoN A. OoLLINs.

